The present invention relates to a gas sensor control device and method.
As a combustion control technique for reduction of CO, NOx and HC exhaust emissions from internal combustion engine e.g. gasoline engine, air-fuel ratio feedback control is widely used to regulate fuel injection in accordance with the concentration of a specific gas component in engine exhaust gas.
There are various exhaust gas sensors for use in the air-fuel ratio control. One example of exhaust gas sensor is an oxygen sensor having a single electrochemical cell in which a solid electrolyte material body is arranged between electrodes to detect the concentration of oxygen in measurement exhaust gas. Another example of exhaust gas sensor is an air-fuel ratio sensor (also called a “universal exhaust gas oxygen sensor”) having two electrochemical cells: a sensing cell and a pumping cell with a measurement gas chamber defined between these electrochemical cells to introduce measurement exhaust gas into the measurement gas chamber through a gas diffusion material and detect the concentration of oxygen in the measurement exhaust gas. A NOx sensor with three electrochemical cells is also known as exhaust gas sensor.
Japanese Laid-Open Patent Publication No. 2003090821 discloses one type of sensor control device that controls energization of the exhaust gas sensor, and more specifically, the sensor cell or cells. In general, the sensor control device provides a plurality of sensor energization modes such as a gas concentration detection mode, a protection mode and a pre-energization mode. The gas concentration detection mode is selected to energize the gas sensor with a relatively large electric current for gas concentration detection. The protection mode is selected to interrupt electrical continuity between the gas sensor and the sensor control device for electrical protection of the gas sensor. The pre-energization mode is selected to pre-energize the gas sensor with a small electric current and thereby activate the gas sensor in readiness for the gas concentration detection mode.